It is often desired to provide a coating, film, or film layer with good optical properties. Some desired optical properties are, for example, clarity, lack of haze, and lack of color. One particularly desirable optical property is relatively low level of yellowness, and it is often desired that the relatively low level of yellowness be maintained upon aging of the coating. Sometimes, the good optical properties are desired because the coating will be applied to a substrate, and it is desired that the appearance of the substrate be altered as little as possible by the presence of the coating. Sometimes, multiple layers of the coating and substrate will be stacked on top of each other, for example when a coated substrate is wound into a roll, and it is desired that the stack thus formed has good optical properties.
US 2002/0082319 discloses 2-stage emulsion polymers made with sodium-based emulsifier, initiator, buffer, and neutralizer, in compositions that also contain low levels of ethylenediametetraacetic acid (EDTA).
The problem faced by the inventors is the provision of aqueous polymer compositions that, when dry, are useful as coatings, have less yellowness than previously known compositions, and maintain their low level of yellowness upon aging. We have found that this problem can be solved by providing aqueous polymer compositions that exclude all or nearly all ammonia compounds from the composition and that include a sufficient amount of at least one coordinating agent in the composition.